This invention relates in general to earth boring drill bits, and in particular to an improved drill bit nozzle for discharging drilling fluid against the bottom of a borehole.
The most common type of bit for drilling oil and gas wells has three rotatable and generally conical cutters. The cutters have teeth that disintegrate the earth's formations during drilling. Fluid is pumped down the drill string and discharged out three outlets in the bit. The fluid cools the bit and circulates cuttings up the borehole to the surface of the earth.
One type of drilling fluid is a liquid slurry known as "mud" that often contains particulates such as abrasive sand particles. Nozzles formed of sintered tungsten carbide are mounted in the fluid outlets of the bit to reduce erosion. Each nozzle is a short cylinder with a converging axial bore. Because of the high pumping pressures and the abrasive mud, the nozzles have to be firmly secured in the outlets to avoid movement. Also, any retainer must be shielded to some extent to avoid erosion. In addition, the exterior wall of the nozzle must be sealed within the outlet to prevent fluid from leaking between the walls of the outlet and the nozzle and eventually eroding the outlet.
One common type of nozzle assembly employs a snap ring located within a groove formed in the outlet immediately below the bottom of the nozzle. If the mud is exceptionally abrasive, a nozzle with a shroud or extended portion may extend down below the snap ring to avoid erosion. For sealing, an O-ring is located within a groove formed in the outlet for sealing against the exterior of the nozzle.
While this nozzle assembly is successful, close tolerances are necessary for locating the grooves for the retaining ring and O-ring. Also, fatigue cracks occasionally result between the shroud of the nozzle, if a shroud is used, and the body of the nozzle.
Another nozzle assembly in use uses a threaded ring for tightening against the nozzle. One type has a ring with a tapered inner bore that wedges against a mating taper formed on the nozzle. While this method rigidly locks the nozzle to the bit, the O-ring for this assembly is still located within a groove in a conventional manner, and thus requires precise machining.